The present invention relates to a transfer foil having a reflecting layer with a fine dimple pattern recorded thereon, for example, a transfer type reflection relief hologram, a reflection relief diffraction grating, etc.
In this application, a first invention relates to an information recording method wherein information recorded on a transfer foil is transferred to a substrate by a thermal recording head, for example, and information that is different from the information originally recorded on the transfer foil is recorded and displayed on the portion of the substrate where the original information has been transferred. The invention also relates to an information recording medium having information recorded thereon by the above-described method.
A second invention relates to a reflection relief hologram transfer foil which is formed in a specific transfer type, and also to a selective transfer method for a reflection relief hologram which employs such a transfer foil. More particularly, the invention relates to a transfer foil which enables a fine hologram pattern to be readily transferred to a large area, and to a transfer method employing such a transfer foil.
A third invention relates to a transfer foil having on the surface thereof an extremely fine dimple pattern, for example, a hologram, a building material, an optical recording medium, etc., which can be transferred in a precise pattern by a hot stamper, a thermal head or the like. The invention also relates to a method of producing such a transfer foil.
Holograms, in which information is recorded generally in the form of interference patterns of light, are used in various fields as high-density information recording media for recording and displaying two- and three-dimensional images and other information. Among them, relief holograms are formed in such a manner that a holographic interference fringe pattern is recorded in the form of a dimple pattern on a photoresist, for example, and the dimple pattern is transferred by plating, for example, to form a stamper, which is then stamped on a transparent thermoplastic resin material with or without a reflecting layer of a metal or the like formed on the surface thereof, thereby making a large number of duplicates. Relief holograms wherein a reflecting layer, e.g., a metal layer or a high refractive index layer, is provided on the relief surface and an image is reconstructed by light reflected and diffracted by the reflecting layer include two different types, in one of which the incident light is reflected substantially completely by the reflecting layer, while in the other part of the incident light is reflected to reconstruct a hologram image on a background of transmitted light. In this application, these two types are included in the reflection relief holograms. In addition, another type of relief hologram in which the dimple pattern comprises phase diffraction grating patterns properly arranged is also considered to be included in the reflection relief holograms.
A typical reflection relief hologram has a sectional structure shown in FIG. 10, and it comprises a hologram layer 1 of a thermoplastic resin material or the like and a reflecting layer 2 formed on a dimple interference fringe surface (i.e., relief surface) defined by the surface of the hologram layer 1. The reflecting layer 2 comprises either a deposited metal film, e.g., aluminum or tin, or a high refractive index transparent film, e.g., zinc sulfide. With a deposited metal film, a reflection relief hologram that reflects the incident light substantially completely by the metal is formed. With a high refractive index transparent film, the resulting reflection relief hologram is of the type in which part of the incident light is reflected to reconstruct a hologram image on a background of transmitted light because of Fresnel reflection based on the refractive index difference between the hologram layer 1 and the reflecting layer 2. Such a reflection relief hologram may be produced by either of the following two methods: one in which holographic information is recorded in the form of a dimple pattern on a photoresist, for example, and the dimple pattern is transferred by plating, for example, to form a stamper, which is then stamped on a transparent thermoplastic resin material that constitutes a hologram layer 1 to duplicate the dimple pattern, and a reflecting layer 2 is formed on the duplicated dimple pattern by deposition or the like; and the other in which a reflecting layer 2 is previously formed on a transparent resin layer that forms a hologram layer 1, and a stamper formed with the above-described dimple pattern is hot-stamped on the reflecting layer 2 to duplicate the dimple pattern (for example, see Japanese Patent Application Laid-Open (KOKAI) No. 58-65466 (1983)).
Incidentally, such a reflection relief hologram can be arranged in the form of a transfer foil (for example, see Japanese Patent Application Laid-Open (KOKAI) No. 01-283583 (1989)). FIG. 11 shows a section of the transfer foil. In order to enable the reflection relief hologram shown in FIG. 10 to be transferable, a base film 4 of PET (polyethylene terephthalate) or the like is provided on the side of the hologram layer 1 opposite to the side thereof where the reflecting layer 2 is provided, through a release layer 3 of wax or the like, and a heat-sensitive adhesive layer 5 of a vinyl chloride resin or the like is provided on the reflecting layer 2. The hologram layer 1 and the reflecting layer 2 in a desired profile region of a transfer foil having the above-described arrangement may be transferred to a substrate of vinyl chloride, for example, by using, for example, a thermal recording head or a hot stamper, as follows: The transfer foil is set in between a substrate 6 to which the hologram is to be transferred and a thermal recording head or hot stamper 7 such that the heat-sensitive adhesive layer 5 faces the substrate 6, while the base film 4 faces the thermal recording head or hot stamper 7, and in this state the thermal recording head 7 is driven or the hot stamper 7 is pressed under heating.
Thus, the reflection relief hologram has heretofore been transferred to the substrate 6, e.g., a card, as shown in FIG. 12, to display visible information, e.g., a mark, an image, etc., on a card or the like. However, it has been impossible to record and display in the transfer region image information, character information, etc. other than the information originally recorded on the transfer foil.
Further, in either the transfer method employing a hot stamper or the transfer method employing a thermal recording head, only the transfer hologram pattern portion is heated from the side of the base film which is remote from the hologram layer, a heat or pressure dispersion phenomenon occurs in the base film, so that it is difficult to reproduce the desired pattern strictly. Thus, the prior art is unsuitable for transfer of a fine pattern.
Incidentally, there has heretofore been a known method of duplicating a large number of transfer foils having an extremely, fine dimple pattern, for example, a relief hologram, a diffraction grating, an optical information recording medium, etc., as described above. According to this method, a resin layer that is provided on a base film through a release layer is softened by heat-pressing to form a dimple pattern, thereby duplicating a large number of transfer foils by embossing.
It is common for most of these dimple pattern transfer foils to form a reflecting layer of a metal or the like by plating technique on a dimple pattern formed on a resin layer in order to enhance the optical effectiveness of the dimple pattern.
However, the method, in which a metal thin film layer is provided on a dimple pattern formed on a resin layer, involves the problem that during the formation of a dimple pattern on the resin layer, the material of the resin layer may be transferred to a dimple forming stamper due to the release resistance occurring between the stamper and the resin layer. If silicone or the like is added to the resin layer to reduce the release resistance of the transfer foil in order to prevent the described problem, the adhesion with a reflecting layer formed subsequently lowers, so that the reflecting layer becomes likely to separate. If the film breaking strength of the resin layer is increased, the release characteristics and foil breaking characteristics required for the transfer process deteriorate, so that it becomes difficult to transfer a fine pattern.
When a dimple pattern is formed on a resin layer of a thermoplastic resin material under heating, there is a need for a process of releasing the resin layer from the stamper after cooling it because it is likely that the dimple pattern formed will be deformed by the heat remaining after the release.
In addition, when a metal thin film layer is formed on a dimple pattern, the dimple pattern may be deformed by heat or chemical influence during plating process or it may be impossible to obtain a reflecting layer with a uniform thickness distribution due to the dimple pattern. It is also likely that mixing of dust will cause a pinhole or adhesion failure. Thus, the prior art suffers from problems in terms of quality.
In addition, when the take-up type semicontinuous deposition method or the like is employed for the formation of a reflecting layer, the process efficiency is inferior in that a reflecting layer is deposited each time the embossing process has been completed, so that it is disadvantageous to small lot products in terms of both cost and time.